Oxy-boiler with steam assisted production

ABSTRACT

Methods and systems relate to an oxy-boiler used to generate steam injected into a well for assisting recovery of hydrocarbons. Operating conditions of a burner for the oxy-boiler limits oxygen contamination in a resulting flue gas for carbon dioxide recovery and limits size of the oxy-boiler, which may thus be located proximate the well rather at a central processing facility. In contrast to a direct steam generation approach where resulting carbon dioxide is mixed with steam, the oxy-boiler also enables selection of a desired level of carbon dioxide injection, which may be provided with the flue gas that may be exhausted from the oxy-boiler at an injection pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/837,686 filed Jun. 21, 2013 entitled “OXY-BOILER WITH STEAM ASSISTED PRODUCTION,” which is incorporated herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

None.

FIELD OF THE INVENTION

Embodiments of the invention relate to generating steam for steam assisted production of hydrocarbons with an oxy-boiler operated to facilitate flue gas applications.

BACKGROUND OF THE INVENTION

Recovery of heavy oil reserves often requires use of steam to heat and mobilize the oil through processes such as steam assisted gravity drainage (SAGD). Energy intensive steam generators produce the steam and resulting carbon dioxide emissions. Government regulations may make capture and sequestration of the carbon dioxide emissions necessary.

Scrubbing flue gases of the steam generators with a carbon dioxide absorbing solution like an amine based mixture offers one prior approach for the capture. However, additional costs associated with capturing the carbon dioxide further increase expenses limiting economic recovery of the oil. Direct steam generation burns fuel with oxygen in presence of water to generate a mixture including steam and carbon dioxide, which may not be at a desired concentration for injection.

Oxy-fuel combustion for steam boilers provides an alternative option for mitigating carbon dioxide emissions since flue gas contains carbon dioxide and water vapor as primary separable constituents. However, recovered carbon dioxide from the flue gas may still require treatment to remove oxygen, nitrogen and argon contaminants in order to meet pipeline and storage specifications. Further, combustion at atmospheric pressure provides the flue gases at pressures too low for injection with the steam.

Therefore, a need exists for systems and processes that enable generating steam with efficient carbon dioxide recovery and utilization.

BRIEF SUMMARY OF THE DISCLOSURE

In one embodiment, a method of steam assisted oil recovery with carbon dioxide control includes generating steam in an oxy-boiler that combusts fuel with oxygen in an environment pressurized to at least 690 kilopascals for producing the steam separate from flue gas resulting from burning of the fuel. Injecting the steam into a formation assists in recovering the oil. The method further includes processing at least part of the flue gas to provide dehydrated and compressed carbon dioxide that is transported to a sequestration site different than the formation.

For one embodiment, a system for steam assisted oil recovery with carbon dioxide control includes an oxy-boiler configured to combust fuel with oxygen in an environment pressurized to at least 690 kilopascals for producing steam separate from flue gas resulting from burning of the fuel. An injection well couples to an output of the oxy-boiler for injecting the steam into a formation to assist in recovering the oil. Further, a pipeline couples to an exhaust of the oxy-boiler for receiving at least part of the flue gas for carbon dioxide transport to a sequestration site different than the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefits thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic of a production system for steam assisted oil recovery utilizing an oxy-boiler with oxygen and excess fuel supplied at pressures above 690 kilopascals, according to one embodiment of the invention.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

Methods and systems relate to an oxy-boiler used to generate steam injected into a well for assisting recovery of hydrocarbons. Operating conditions of a burner for the oxy-boiler limits oxygen contamination in a resulting flue gas for carbon dioxide recovery and limits size of the oxy-boiler, which may thus be located proximate the well rather at a central processing facility. In contrast to a direct steam generation approach where resulting carbon dioxide is mixed with steam, the oxy-boiler also enables selection of a desired level of carbon dioxide injection, which may be provided with the flue gas that may be exhausted from the oxy-boiler at an injection pressure.

FIG. 1 illustrates an exemplary system that includes an oxy-boiler 100, an injection well 101, a production well 102, and a separator 104. While illustrated in an exemplary SAGD configuration, other techniques, such as cyclic steam stimulation, solvent assisted SAGD, steam drive or huff and puff, may employ the steam generated as described herein. The injection well 101 extends in a horizontal direction and above the production well 102 also extending in the horizontal direction.

In operation, steam generated by the oxy-boiler 100 enters a formation along the injection well 101 forming a steam chamber with heat transferred from the steam to oil or bitumen in the formation. The oil once heated becomes less viscous and mobile enough for flowing by gravity along with condensate of the steam to the production well 102. A mixture of the condensate and oil collected in the production well 102 flows to surface where the oil to be sold is removed in the separator 104 from the condensate, which is recycled for generating additional steam to sustain steam injection.

The oxy-boiler 100 receives fuel and oxygen combusted at a burner to heat water that is input and maintained separate from resulting combustion products that exit the oxy-boiler as flue gas. The heat from the burner transfers across a boiler vessel such as tubes containing the water. At least part of the water converts to steam that may have a quality of at least seventy-five percent and may be separated from remaining liquid blowdown prior to being conveyed into the injection well 101.

Examples of the fuel input into the oxy-boiler 100 include hydrocarbons such as coal, petroleum coke, asphaltenes, methane or natural gas. In some embodiments, a feed of the oxygen supplied to the oxy-boiler 100 contains at least 95% by volume pure oxygen separated from air. For some embodiments, the oxy-boiler 100 operates under stoichiometric conditions with respect to the fuel and oxygen or fuel-rich conditions to at least limit oxygen carryover into the flue gas.

In some embodiments, the fuel and the oxygen further enter the oxy-boiler 100 pressurized to above 690 kilopascals (kPa), between 690 kPa and 1040 kPa, or up to 6900 kPa. Pressurization of an environment where the fuel is burned and the flue gas may correspond and be at least 690 kilopascals (kPa), between 690 kPa and 1040 kPa, or up to 6900 kPa. This pressurization helps prevent air leakage into the oxy-boiler 100. As fuel/oxygen feed and combustion pressures approach atmospheric levels, some oxy-combustor sections may operate under vacuum resulting in the air leakage and contamination of the carbon dioxide in the flue gas with oxygen from the air that gets entrained into the flue gas.

The pressurization from the fuel and the oxygen supplied to the oxy-boiler 100 also limits size or footprint of the oxy-boiler 100 required to generate a given amount of the steam. In particular, such pressurized burning relative to atmospheric increases heat transfer and decreases flue gas velocity such that the water can be heated within a smaller volume in the oxy-boiler 100. In some embodiments, the footprint of the oxy-boiler 100 enables locating the oxy-boiler 100 on a pad with restricted space proximate the injection well 101 rather than at a central processing facility.

The central processing facility may supply the water, fuel and oxygen to the oxy-boiler at the pad. The oxy-boiler 100 located at the pad limits heat losses along steam lines since the oxy-boiler 100 may be within 100 meters of the injection well 101 compared to the central processing facility that may be greater than 100 meters from the injection well 101. Further, generating the steam at the pad extends possible distance between the pad and the central processing facility since not limited by such heat loss along steam lines.

Regarding the flue gas, a first portion of the flue gas may recycle back to the burner and may mix with the oxygen for moderating flame temperatures in the oxy-boiler 100 to levels common during conventional combustion and within thermal thresholds. A recycle blower may facilitate achieving desired flow of the flue gas for such recirculation. In some embodiments, a second portion of the flue gas may flow into the formation to promote recovery of the hydrocarbons. For example, the carbon dioxide may reduce viscosity of the hydrocarbons upon dissolving in the hydrocarbons.

For some embodiments, the second portion of the flue gas injected into the formation mixes with the steam before being conveyed into the formation through the injection well 101. The pressure of the combustion in the oxy-boiler 100 in some embodiments produces the flue gas at desired injection pressures (e.g., 5000 kPa to 11,000 kPa) without requiring further processing. The flue gas contains both water vapor from combustion products and the carbon dioxide that may be injected such that the second portion of the flue gas may contribute to water makeup requirements.

For configurations in which the flue gas pressure is lower than the desired injection pressure, the second portion of the flue gas may pass to a processing unit before being injected. The processing unit cools and compresses the flue gas to the injection pressure. Use of the oxy-boiler 100 at the pad for the injection well 101 provides the second portion of the flue gas also at the pad such that transport of carbon dioxide to be injected may not be required to come from the central processing facility.

The flue gas emitted from the oxy-boiler 100 splits between the second portion for injection and a third portion sent back to the central processing facility for subsequent transport to an offsite storage site. Amount of the flue gas in each of the second and third portions depends on desired carbon dioxide injection levels for a particular application. Unlike direct steam generation techniques with limited ability to control the carbon dioxide injection levels, embodiments of the invention may enable controlling the carbon dioxide injection levels all the way down to zero by diverting all the flue gas emitted to the third portion. For example, the steam and carbon dioxide mixture injected into the formation thus may contain less than 9%, less than 5% or less than 3% carbon dioxide by weight.

For some embodiments, the third portion of the flue gas passes to the central processing facility and is processed prior to being introduced into a carbon dioxide pipeline or otherwise transported for use or sequestration offsite. Processing of the third portion of the flue gas may include dehydrating and compressing the carbon dioxide. Any water recovered from the third portion of the flue gas may also contribute to supplying makeup water to the oxy-boiler 100.

The carbon dioxide may make up by volume at least about 85%, at least about 90%, or at least about 95% of the flue gas. The fuel-rich conditions and/or the pressurized combustion may provide the flue gas with oxygen content of below 0.001% by volume and thereby below pipeline or transport specifications. Since below such maximum oxygen content thresholds, the flue gas may not require an expensive oxygen removal treatment.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention.

Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents. 

1. A method of steam assisted oil recovery with carbon dioxide control, comprising: generating steam in an oxy-boiler that combusts fuel with oxygen in an environment pressurized to at least 690 kilopascals for producing the steam separate from flue gas resulting from burning of the fuel; injecting the steam into a formation to assist in recovering the oil; processing at least part of the flue gas to provide dehydrated and compressed carbon dioxide; and transporting the carbon dioxide to a sequestration site different than the formation.
 2. The method according to claim 1, further comprising injecting a portion of the flue gas into the formation.
 3. The method according to claim 1, wherein quantity of the fuel and oxygen supplied to the oxy-boiler for the burning is stoichiometric.
 4. The method according to claim 1, wherein quantity of the fuel and oxygen supplied to the oxy-boiler for the burning is fuel-rich.
 5. The method according to claim 1, wherein the flue gas upon emission from the oxy-boiler contains less than 0.001% oxygen by volume.
 6. The method according to claim 1, wherein the oxy-boiler is disposed within 100 meters of where the steam is introduced into a well for the injecting into the formation.
 7. The method according to claim 1, wherein quantity of the fuel and oxygen supplied to the oxy-boiler for the burning is one of stoichiometric and fuel-rich and the oxy-boiler is disposed within 100 meters of where the steam is introduced into a well for the injecting into the formation.
 8. The method according to claim 1, further comprising injecting into the formation a portion of the flue gas uncompressed after pressurized emission from the oxy-boiler.
 9. The method according to claim 1, further comprising compressing a portion of the flue gas prior to injection into the formation.
 10. The method according to claim 1, wherein fluids injected into the formation including the steam and a portion of the flue gas form a mixture containing less than 9% carbon dioxide by weight.
 11. The method according to claim 1, wherein fluids injected into the formation including the steam and a portion of the flue gas form a mixture containing less than 5% carbon dioxide by weight.
 12. A system for steam assisted oil recovery with carbon dioxide control, comprising: an oxy-boiler configured to combust fuel with oxygen in an environment pressurized to at least 690 kilopascals for producing steam separate from flue gas resulting from burning of the fuel; an injection well coupled to an output of the oxy-boiler for injecting the steam into a formation to assist in recovering the oil; and a pipeline coupled to an exhaust of the oxy-boiler for transporting carbon dioxide from at least part of the flue gas to a sequestration site different than the formation.
 13. The system according to claim 12, wherein the injection well is further coupled to the exhaust of the oxy-boiler for injecting a portion of the flue gas into the formation.
 14. The system according to claim 12, wherein the oxy-boiler is configured to input stoichiometric quantities of the fuel and oxygen for the burning.
 15. The system according to claim 12, wherein the oxy-boiler is configured to input fuel-rich quantities of the fuel and oxygen for the burning.
 16. The system according to claim 12, wherein the oxy-boiler produces the flue gas with less than 0.001% oxygen by volume.
 17. The system according to claim 12, wherein the oxy-boiler is disposed within 100 meters of the injection well.
 18. The system according to claim 12, wherein the injection well is further coupled to the exhaust of the oxy-boiler for injecting into the formation a portion of the flue gas uncompressed after pressurized emission from the oxy-boiler.
 19. The system according to claim 12, wherein the injection well is further coupled to the exhaust of the oxy-boiler such that fluids injected into the formation including the steam and a portion of the flue gas form a mixture containing less than 9% carbon dioxide by weight.
 20. The system according to claim 12, wherein the injection well is further coupled to the exhaust of the oxy-boiler such that fluids injected into the formation including the steam and a portion of the flue gas form a mixture containing less than 5% carbon dioxide by weight. 